Z01 HD 001123 LCE and Z01 HD 001124 LCE are companion projects that together investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two non-human primates, the squirrel monkey and common marmoset, are the main subjects of study, with additional data collected from other species where appropriate. Prior work in this project has shown that production of sounds that are the functional and acoustic equivalents of cry sounds in human infants are mediated by limbic cortex located along the anterior midline of the frontal lobe of the cerebral cortex, and that single neural elements in the auditory cortex (superior temporal gyrus) are particularly responsive to subtle differences in the acoustic structure of species-specific vocalizations, suggesting an important role in mediating individual differences (vocal signatures). New findings this year: The gene c-fos and its protein product Fos, have been used to mark neural regions of increased activity following a period of robust behavioral activity. A study of c-fos expression in adult squirrel monkey brains was conducted. The paradigm involved separating individuals for 30 minutes, recording the ?isolation calls? made during this separation, returning them to their home cage for 1 hour, then euthanizing them and processing their fixed brains for Fos using immunocytochemistry. Six individuals were used, 3 good vocalizers and 3 poor vocalizers (less than 10 calls in 30 minutes). Microphotographs at 200 magnifications were digitized, then labelled cells counted. Fields from 3 brain areas were compared between good vocalizers and poor vocalizers. The 3 areas were the anterior cingulate gyrus, the perventricular/periaqueductal gray, and the dorsomedial thalamus. The first 2 were found in a study using brain lesioning to be involved in expression of calls in separated squirrel monkeys; the last is known to be a projection area to the anterior cingulate, but was not included in the earlier study. Counts of labelled cells were significantly different between all 3 areas in the brains of good and poor vocalizers. In all cases, counts were higher in the good vocalizers. These results indicate that c-fos immunocytochemistry is a valid alternative to demonstrating the functional involvement of primate brain regions involved in vocalizing, and has the advantage of labelling structures throughout the neuraxis in a single animal, whereas older techniques such as lesioning require many more animals to give a clear result. In a second study, a new method for creating schematic brain images was developed as part of the creation of a brain atlas for the common marmoset. Digital photographs of frontal sections from an adult female marmoset were set to a standard size using Adobe Photoshop. The images were then imported into ImageJ, a program developed at the NIH. By inverting the image and using the ?find edges? tool, an outline version of the image was created. The internal structure of these schematic images could still be discerned and labelled. This permitted retention of the original digital photograph, without the distraction of any added labels. At the same time, individual structures within the brain section could be identified in the schematic image, allowing future users of the atlas to find their way around a given brain section. This work was done by Ms. Rachel Bell, a student at Montgomery Blair High School, in a collaboration between the UNE and Dr. Afonso Silva of the NINDS.